Electronic Structure of Self-Assembled Monolayers Modified with Ferrocene on a Gold Surface: Evidence of Electron Tunneling

The electron transfer mechanism for the prototypical system ferrocenoyl-glycylcystamine (Fc-Gly-CSA) on Au(111) is investigated within the framework of density functional theory. Different Fc-Gly-CSA/Au systems, including the explicit methanol solvent and sodium perchlorate counterion, are studied. As seen from the partial density of states, electronic contributions close to the Fermi energy are found to derive only from the ferrocene units and gold atoms, while the contributions from electronic states located on the molecular spacers (Gly-CSA) are detected at lower energies, with or without the effects of the environment. These results strongly indicate a direct ferrocene-to-gold tunneling as the electron transfer mechanism across the interface.